Light and Temperature Relations in a Small Desert Pond as Influenced by Phytoplanktonic Density Variations

Measurements of incoming and reflected solar radiation, down‐welling solar radiation in the water, and air temperature and water temperature at four different depths were recorded every half hour over a 3‐month period in a small man‐made pond of reclaimed waste water at Phoenix, Arizona. At intervals of a few days, chlorophyll a and b values were also assayed to determine density variations in the phytoplanktonic community of the pond. During this period the extinction coefficient far solar radiation was found to be a linear function of both chlorophyll a and b concentrations, and the shape of the midafternoon temperature profile of the pond was found to be highly correlated with the extinction coefficient. Water surface temperature increased during three distinct algal blooms to such a degree that the water‐air vapor pressure difference increased by approximately 25% during the short periods of the blooms, an indication that phytoplanktonic density variations may exert a significant influence on evaporation.